Field of the Invention
The present invention relates to laboratory apparatus and method for characterizing ionic and nonionic condensation from a complex vapor stream.
Background of the Related Art
Since the first crude oil refineries began operating over 150 years ago, corrosion has been experienced in the vessels used to separate the crude oil into saleable products. Early technology involved a series of separation vessels called pipe stills that would sequentially remove fractions based on boiling point, increasing from lowest to highest. Since a high production rate was more important than the life of the equipment at that point in time, corrosion did not initially receive much focus. However, after the invention of the automobile, refineries became larger and more integrated with upgraded processes. Accordingly, the refinery downtime that was necessary to replace corroded equipment became more costly and corrosion control became more important.
Early attempts to control corrosion focused on filming inhibitors and use of ammonia. The ammonia was added to raise the pH of the overhead water, which contains hydrochloric acid (HCl) as a by-product of crude oil distillation. The classic hydrolysis of salt found in crude oil is shown in Equations (1), (2), and (3), below. The third reaction contributes very little to the HCl in the overhead, because the hydrolysis temperature of NaCl is higher than typical crude heater to fractionator transfer temperatures.MgCl2+H2O→Mg(OH)2+2HCl  Equation (1):CaCl2+H2O→Ca(OH)2+2HCl  Equation (2):NaCl+H2O→NaOH+HCl  Equation (3):
Salting by ammonium chloride was recognized for its fouling and corrosion, but was initially dealt with by regular washing of equipment. However, washing required either a brief shutdown or a slowdown in operations, both of which became unacceptable as the economics of refinery operation became more competitive. Over time, other attempts at overhead corrosion control included the addition of alkaline metals or the addition of morpholine, which were intended to control the acidity of the first condensate. Originally this first condensate was characterized using equilibrium vapor pressures. It was recognized that as a pure compound, water would condense quickly from steam mixed with naphtha. The temperature at which water would begin to cascade out of the vapor became known as the Water Dew Point (WDP).
Despite the use of neutralizers and filming inhibitors, the corrosion problems in the overhead condensing equipment and in cold towers continued. A 1985 NACE survey showed that the average life for a bundle in overhead condensing service was about seven years. Various amines have also been used to control corrosion in the overhead condensing equipment, but have been found to cause the formation of amine chloride salts ahead of the WDP, similar to what was known to occur with ammonia in the presence of the HCl.